It is proposed to develop the chemical and analytical potential of mass spectrometry for applications to constituents of nucleic acids and their analogs. Techniques which will be studied include combination gas chromatography-mass spectrometry, chemical ionization, and high resolution mass spectrometry. Mass chromatography and multiple ion detection techniques will be used in conjunction with stable isotope labeling for qualitative and quantitative analysis in the 10 to the minus 6th power - 10 to the minus 12th power gram range. These methods will be applied to selected problems involving location of nitrogen-15 in purines; sequence of oligonucleotides; structural studies of modified nucleosides from Novikoff hepatoma ascites cells and from E. coli; studies of structure and biosynthesis of polyoxin nucleoside antibiotics; and the identification of metabolites of the antitumor drug 1-(tetrahydro-2-furanyl)-5-fluorouracil in the rat.